Solid propellant with non-metallic burning rate catalysts

ABSTRACT

A NEW GROUP OF BURNING RATE CATALYSTS USED IN SOLID COMPOSITE PROPELLANT COMPOSITIONS. THESE CATALYSTS ARE NON-METALLIC HIGH MOLECULAR WEIGHT ALDLEHYDES OR KETONES PREFERABLY HAVING AT LEAST EIGHT CARBON ATOMS PER MOLECULE, OR NON-METALLIC SUBSTITUTED PHENOLS. TYPICAL COMPOUNDS OF THIS TYPE OF CATALYST ARE OCTADECENYLALDEHYDE, BETA-METHYLUMBELLIFERONE, 3,3,5-TRIMETHYLHEXALDEHYDE, NORMAL-DECYLALDEHYDE, PARA-HYDROXYPROPIOPHENONE, 2ETHYLHEXALDEHYDE, OCATADECYL ALDEHYDE, 8-HEPTADECYLKETONE, PENTACHLOROPHENOL, AND PARA-HYDROXYVBENZALDEHYDE.

United States Patent 01 :"fice 3,811,964 SOLID PROPELLANT WITH NON-METALLIC BURNING RATE CATALYSTS David C. Sayles, Huntsville, Ala., assignor to the United States of America as represented by the Secretary of the Army No Drawing. Filed Dec. 11, 1968, Ser. No. 783,155

Int. Cl. C06d 5/06 US. Cl. 14919.1 6 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to a new group of burning rate catalysts used in solid composite propellant compositions, and in particular to such a group which is non-metallic.

The need for solid composite propellant compositions which have ultra-high burning rates is Well established. In the past, high percentages of organometallic compounds such as ferrocene, normal-butylferrocene and similar compounds have been incorporated in solid composite propellant compositions to achieve the desired ultra-high burning rates. However, these organometallic compounds have not been entirely satisfactory. In particular, the use of organometallic compounds (or metallic compounds) in propellant compositions produces particulate matter (e.g., the oxides of iron) in the rocket exhaust upon combustion. The solid particles thus produced create large quantities of visible smoke. Smoke is highly undesirable for military purposes of concealment. Organometallic compounds useful as burning rate catalysts are generally more expensive than nonmetallic organic compounds. Hence, non-smoky, non-metallic organic burning rate catalysts are preferred for military purposes. Unfortunately, propellant compositions utilizing conventional non-metallic organic burning rate catalysts have heretofore exhibited only relatively slow burning rates.

SUMMARY OF THE INVENTION It has been discovered that the burning rates of solid composite propellant compositions can be markedly increased through the use of certain non-metallic organochemical burning rate catalysts. In general these organochemicals are high molecular weight aldehydic, ketonic, compounds preferably having eight or more carbon atoms per molecule, or substituted phenols. Examples are octadecyl aldehyde, beta-methylumbelliferone, para-hydroxypropiophenone, pentachlorophenol, para-hydroxybenzaldehyde, octadecenylaldehyde, 3,3,S-trimethylhexaldehyde, normal-decylaldehyde, 2-ethylhexaldehyde, and 8-heptadecylketone.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The solid composite propellant compositions of this invention achieve ultra-high burning rates through the incorporation therein of minor amounts of certain nonmetallic organochemicals functioning as burning rate catalysts. In general, these organochemicals are high 3,811,964 Patented May 21, 1974 molecular weight aldehydic or ketonic compounds, having eight or more carbon atoms per molecule, or substituted phenols. Typically, from about 0.5 percent to about 7 percent, by weight, of one of these organochemical compounds, or mixtures thereof, is incorporated in a solid composite propellant composition to achieve the ultra-high burning rates desired.

Examples of these compounds are octadecyl aldehyde, beta-methylumbelliferone, para-hydroxypropiophenone, pentachlorophenol, para-hydroxybenzaldehyde, octadecenylaldehyde, 3,3,S-trimethylhexaldehyde, normal-decylaldehyde, Z-ethylhexaldehyde, and S-heptadecylketone.

The structural formula of these compounds follow:

para-hydroxyproplophenone O HoOd-wHr-om pentachloro henol p OH.

para-h drox benzaldeh de Y Y Y CH0 octadecenylaldehyde CH (CH2) 7CH=CH(CH2) 7-CHO 3,3,5-trimethylhexaldehyde CH: CH:

CHr-CHCHrCH-CHCHO n ormal-decylaldehyde 2-ethylhexaldehyde CHz-(OHflr-CHO CHa-(CHDrCH-CHO H: 8-heptadecylketone [CH3(CHI)7]2C=O The burning rate catalysts of this invention can be aliphatic or aromatic aldehydes or ketones. If an aliphatic aldehyde or ketone is employed, it should have at least eight carbon atoms per molecule. If an aromatic aldehyde or ketone is employed, it need not have eight carbon atoms per molecule. Although almost any aromatic aldehyde or ketone can be employed, it should preferably also be a phenol (for maximum elfectivcness).

The burning rate catalysts of this invention can also be substituted phenols. Although a phenol (for use in accordance with this invention) also having an aldehydic or ketonic function (or both) can be of almost any type or amount of substitution, a phenol (for use in accordance with this invention) not having an aldehydic or ketonic function should preferably be substituted with a. high molecular weight substituent (e.g., halogens), have a long chain substituted thereon, preferably, branched chain hydrocarbon (e.g., tert.-, sec.-butyl or the like), be substituted generally at more than one position, or prefer ably have a combination of at least two of these substitution factors. A substitution factor means a substituent. For example, a suitable substituent to a compound containing a phenolic group, but not containing an aldehydic or ketonic function, may be selected from the radical groups: halogens, branched chain aliphatic hydrocarbons, and substituted branched chain aliphatic hydrocarbons. Examples of branched chain aliphatic hydrocarbon substituted phenols are as follows: 2,4,6-tri(tert.-butyl) phenol, 2,4,6-tri(sec.-butyl)phenol, and p-tert.-butylphe- I101. The substituent having branched chains may be also a radical group having substituents therein. The substituents therein may be selected from halogens, other nonmetallic elements, hydrocarbon radicals, and substituted hydrocarbon radicals. Substitution to a phenol of the high molecular weight groups, such as those described, renders a phenol useful as a catalyst for this invention. Phenol can be highly substituted since it contains five primary substitution positions or positions to which substituents may be located. For example, five chlorine atoms react with phenol to form pentachlorophenol. The compound is prepared by the chlorination of phenol which results in chlorine being substituted for hydrogen. The total molecular weight increase to phenol by the substituents, five chlorine atoms, amounts to about 172. Thus, the molecular weight increase to phenol can be adjusted to cover a wide range by selecting from the substituent radical groups specified above by making a single substitution or by making a plurality of substitutions to the phenol. The molecular weight increase to phenol by the substituent groups specified is a means of rendering a phenol compound useful as a catalyst for this invention.

The molecular weight increase by means of substituents specified decreases the tendency of a phenol to become oxidized. Additionally, steric hindrance is accomplished by the substituents to interfere with early reaction (oxidation or chemical attack) at the hydroxyl group of the phenolic compound. Preventing early reaction at the hydroxyl group gives longer storage life to the propellants containing the substituted phenolic type catalysts. The substituted phenols provide a longer reaction time when burned than do the non-substituted phenols; the catalytic action is available during the complete burning period of the propellant. Other properties, such as melting points and boiling points, are substantially altered as recognized by the examples set forth below. The melting points and boiling points of phenol are 42 C. and 182 C. respectively. A single substituted chlorine atom to phenol yield o-monochlorophenol which Was a melting point of 7 C. and boiling point of 173 C. Five substituted chlorine atoms to phenol yields pentachlorophenol which has a melting point of 188 C. and a boiling point of 310 C. with decomposition. The compound, 2,4,6-triiodophenol, having three substituted iodine atoms, melts at 156 C. Thus, the melting point and boiling point of phenol can be altered over a wide range depending on the type substituent and the degree of substitution made to the compound. A blend of the substituted phenol compounds may be selected to provide many varied compositions for use as catalysts in accordance with this invention. The high molecular weight of these burning rate catalysts and the substitution of the phenolic type catalysts insures that a low volatility and a high solvency of the compound is achieved, thereby making the catalyst compatible (in a physical properties sense) with the other ingredients incorporated in the propellant composition.

Of course, care must be exercised that the burning rate catalyst of this invention is chosen to be chemically compatible with the other ingredients of the propellant composition.

The solid composite propellant compositions of this invention also contain, in addition to the novel burning rate catalyst, a combustible organic resin fuel and an oxidizer, preferably a solid, inorganic, oxidizing salt.

Oxidizers useful in the practice of this invention are nonmetallic chlorate, perchlorate, and nitrate salts such as ammonium nitrate, ammonium chlorate, ammonium perchlorate and hydrazine nitrate. The non-metallic nitrate salts, however, usually do not burn as rapidly as the chlorate or perchlorate salts.

The oxidizer, in a finely divided condition, is dispersed throughout the fuel component of the propellant. Ordinarily, the oxidizer is present in an amount of from about 45% to about 90% by weight of the total composition.

Combustible organic resinous fuel binders useful in propellant compositions of this invention include: polymers and copolymers of alkenes, alkenyl and alkanyl glycols, alkenoic acids and alkanoic acids, and derivatives thereof.

Ordinarily, the fuel binder is present in an amount of from about 10% to about 25% by weight of the total propellant composition.

The fuel binder is generally formed from a monomer(s) or prepolymer. Generally, a crosslinking agent and a polymerization catalyst are also employed.

The following propellant compositions illustrate this invention. Composition A is a propellant composition which has been developed as a high burning rate formulation. Replacement of the normal-butylferrocene with an equivalent quantity of one of the compounds of this invention is illustrated in composition B.

PROPELLANT FORMULATIONS CONTAINING OCIADEC- ENYLALDEHYDE ASA REPLACEMENT FOR N-BUIYL- FERROOENE C ompositi on Ingredient Ammonium perchlorate Aluminum n-Buty1ferroeene Oetadccenylaldehydc Carboxyl-terminatcd polybutadiene prepolymer. Tris(methylazirldinyl)-phosphine oxide Tris(oxiranyl)-pa.ra-amino phenol... Iron linoleato..

Lecithin The average burning rate of propellant composition A is 3.2 inches per second (i.p.s.) under chamber pressure of 2000 psi. Propellant samples using compounds of this invention show a burning rate of from 11-25% increase above the average burning rate of propellant composition A used as a standard. The burning rate of composition B has a burning rate of 3.6 to 4.0 (i.p.s.) under chamber pressure of 2000 p.s.i.

In preparing the propellant compositions of this invention, the various monomers, oxidizer, burning rate catalyst, polymerization catalyst, and crosslinking agent(s) together with any other ingredients desired, are mixed together until a homogeneous mixture is obtained, and the mixture is then cured in a mold by heating. Typically, heating at a temperature of about C. for a period of about 5 days is sufficient to form the desired final propellant composition.

The polymerization catalysts usually employed in such propellant compositions are of the aziridinyl type and the oxiranyl type. Examples are tris(methylaziridinyl) phosphine oxide and tris(oxiranyl)-para-aminophenol.

Various other ingredients can also be added for specific purposes without departing from the scope of the invention. For example, lecithin can be added to improve the castability of the uncured propellant.

The particular fuel employed in the propellant composition does not affect the function of the burning rate acceleration catalyst of this invention.

Although the organochemicals of this invention are particularly attractive for use in smokeless, non-aluminized solid composite propellant compositions the burning rates of aluminized as well as non-aluminized solid composite propellant compositions can be markedly increased through the use of the organochemical compounds of this invention.

The organochemical compounds of this invention can also be used in conjunction with the organometallic compounds already mentioned (ferrocene, normal-butylferrocene, etc.) or other burning rate catalysts.

I claim:

1. A solid composite propellant composition comprising a cured intimate mixture of from about 45% to about 90% by weight solid, non-metallic, inorganic, oxidizin salt, from about to about 25% by Weight combustible organic resin, and from about 0.5% to about 7% by weight non-metallic burning rate catalyst, said catalyst being comprised of at least one compound selected from the following groups of compounds consisting of betamethylumbelliferone and para-hydroxypropiophenone, a high molecular weight aliphatic aldehyde having at least eight carbon atoms per molecule, a high molecular weight aliphatic *ketone having at least eight carbon atoms per molecule, and a substituted phenol, the substituents thereof being selected from the group consisting of halogens and branched chain aliphatic hydrocarbons.

2. The solid propellant composition of claim 1 and wherein said burning rate catalyst is said substituted phenol.

3. The solid propellant composition of claim 1 wherein said burning rate catalyst is said high molecular weight aliphatic ketone having at least eight carbon atoms per molecule.

4. The solid propellant composition of claim 1 and wherein said burning rate catalyst is said high molecular weight aliphatic aldehyde having at least eight carbon atoms per molecule.

5. The solid propellant composition of claim 1 and wherein said burning rate catalyst is comprised of a compound selected from the compounds consisting of octadecyl aldehyde, beia-methylumbelliferone, parahydroxypropiophenone, pentachlorophenol, para-hydroxybenzaldehyde, octadccenylaldehyde, 3,3,5-trimethylhexaldehyde, normal-decylaldehyde, 2-ethylhexaldehyde, and S-heptadecylketone.

6. The solid propellant composition of claim 5 and wherein said catalyst is comprised of a combination of said compounds.

References Cited UNITED STATES PATENTS Re. 26,468 10/1968 Sutton 149-19 3,126,701 3/1964 Henderson ct a1. l4919 X 3,151,010 9/1964 Bice 149-19 3,154,449 10/1964 Ives 149-19 3,498,856 3/1970 Harris 14919 CARL D. QUARFORTH, Primary Examiner E. A. MILLER, Assistant Examiner U.S. Cl. X.R. 149-36, 44, 60, 76 

